Direct semiconductor contact ebullient cooling package

ABSTRACT

The semiconductor package as well as a method for making it and using it is disclosed. The semiconductor package comprises a semiconductor chip having at least one heat-generating semiconductor device and a volumetrically expandable chamber disposed to sealingly surround the semiconductor chip, the volumetrically expandable chamber filled entirely with a non-electrically conductive liquid in contact with the semiconductor device and circulated within the volumetrically expandable chamber at least in part by the generated heat of the at least one semiconductor device to cool the at least one semiconductor device.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a divisional of U.S. patent application Ser. No.11/602,605, entitled “DIRECT SEMICONDUCTOR CONTACT EBULLIENT COOLINGPACKAGE,” by Andrew G. Laquer et al., filed Nov. 21, 2006, and which ishereby incorporated by reference herein.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to systems and methods for packaging andcooling semiconductors, and in particular to a system and method forcooling semiconductors using direct contact semiconductor ebullientcooling.

2. Description of the Related Art

Processor speeds have increased dramatically over the past severaldecades. To achieve such speeds, processors are clocked at increasinglyhigher clock speed and are designed with greater and greater numbers anddensities of semiconductor devices. One difficulty with the higher clockrates and higher densities is that the semiconductor chips that make upsuch processors can generate heat in amounts sufficient to damage thechip itself unless passive or active cooling techniques are employed.Indeed, the rate at which heat can be removed from such semiconductorsis a major factor limiting the maximum processing speed of such devices.This problem is exacerbated by the fact that the chips are also rathersmall, and the heat is concentrated in very small areas and can includevery high temperatures.

High power amplifier semiconductor chips face similar heat dissipationchallenges that limit their power output. The heat must be rapidlytransferred from the semiconductor crystal to the semiconductor packageand safely away from the semiconductor package via a heatsink or someother heat dissipating device.

Most current semiconductor packages utilize only conduction coolingpaths to transfer heat away from the semiconductor device to the packageand then to a heat sink or other heat dissipating device. Such coolingtechniques do not create the thermal paths with sufficient heat flux topermit the higher clock speeds and higher power demanded of current andprojected processor and high power amplifier packages.

What is needed is a cooling apparatus and technique that inexpensivelyprovide very high heat flux thermal paths to dissipate heat fromsemiconductor environments. The present invention satisfies this need.

SUMMARY OF THE INVENTION

To address the requirements described above, a semiconductor package isdisclosed herein. The semiconductor package comprises a semiconductorchip having at least one heat-generating semiconductor device and avolumetrically expandable chamber disposed to sealingly surround thesemiconductor chip, the volumetrically expandable chamber filled with anon-electrically conductive liquid in contact with the semiconductordevice and circulated within the volumetrically expandable chamber atleast in part by the generated heat of the at least one semiconductordevice to cool the at least one semiconductor device. In anotherembodiment, a method of cooling a semiconductor device is disclosed. Themethod comprises the steps of absorbing heat from a semiconductor devicevia a non-electrically conductive inert liquid in contact with thesemiconductor device, sealingly enclosing the semiconductor device andthe non-electrically conductive inert liquid in a volumetricallyexpandable chamber, and passively circulating the non-electricallyconductive inert liquid within the volumetrically expandable chamber atleast in part by the heat drawn from the semiconductor device. In yetanother embodiment, the method comprises the steps of sealinglysurrounding the semiconductor device in a volumetrically expandablechamber, filling the volumetrically expandable chamber with anon-electrically conductive liquid that contacts the semiconductordevice, and passively circulating the non conductive liquid within thevolumetrically expandable chamber by the generated heat of thesemiconductor device to cool the semiconductor device.

The foregoing provides a low cost, heat transfer solution that isamenable to high volume production and can be used to improve theperformance of virtually any integrated circuit, micro miniatureintegrated circuits, or other device who's performance is limited byheat flux. This includes currently available commercial integratedcircuits that can be repackaged and operated for higher performance. Forexample, using the heat transfer techniques described below, arepackaged PENTIUM processor may be clocked at double or triple it'scurrent clock rate, or amplifiers can be operated to provide greaterpower output. Further, future amplifier/processors can be designed fromthe ground up to take greater advantage of the greater heat transferoffered using these techniques.

BRIEF DESCRIPTION OF THE DRAWINGS

Referring now to the drawings in which like reference numbers representcorresponding parts throughout:

FIG. 1A is a diagram of a classical semiconductor package;

FIG. 1B is a plot of a pool boiling curve;

FIG. 2 is a diagram illustrating one embodiment of the presentinvention;

FIG. 3 is a diagram illustrating one embodiment of how the chamber canbe filled with the non-electrically conductive liquid;

FIG. 4 is a diagram illustrating an embodiment wherein the semiconductorpackage uses a flip-chip configuration;

FIG. 5 is a diagram illustrating an embodiment in which the volumetricexpansion is provided by an auxiliary chamber;

FIG. 6 is a diagram showing an embodiment in which a plurality ofsemiconductor devices and packages are cooled in a single volumetricallyexpandable chamber;

FIG. 7A is an illustration of another alternate embodiment of theinvention in which multiple semiconductor assemblies with separatesubstrates are disposed in the volumetrically expandable chamber;

FIG. 7B is an illustration of an embodiment in which thenon-electrically conductive liquid is actively circulated within thevolumetrically expandable chamber; and

FIG. 8 is a diagram of a further alternate embodiment of the invention

DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS

In the following description, reference is made to the accompanyingdrawings which form a part hereof, and which is shown, by way ofillustration, several embodiments of the present invention. It isunderstood that other embodiments may be utilized and structural changesmay be made without departing from the scope of the present invention.

FIG. 1A is a diagram of a classical semiconductor package 100. Thesemiconductor package 100 is produced by bonding a semiconductor chip105 having a semiconductor device 104 (such as a transistor) on asubstrate/heatsink, or packaging surface 108 with an epoxy or eutectic(solder) bond 106 to form a semiconductor assembly 102. The substrate108 is then covered by bonding a portion of it to a lid or cover 110 viaan epoxy, Eutectic (solder) or hermetic weldment 112. In doing so, thechip 105 is hermetically sealed in a small chamber 116 that is filledwith a gas (typically nitrogen). In operation, the heat generated in thesemiconductor device 104 flows from its surface, through thesemiconductor chip 105, through the epoxy or solder bond 106 and intothe substrate 108 or package/heat sink underneath it. Heat transferredto the cover 110 can be drawn away by an optional heat sink 114 whichcan be on the top or the bottom of the assembly.

What is needed is a design that transfers heat from the semiconductor104 to the package 100 faster, but maintain the sealed environment, allin a low cost package that does not require active cooling.

Gases conduct heat poorly, but are easy to seal inside a semiconductorpackage 100 because they are compressible. Liquids can be good heatconductors but most are not compatible with semiconductor operations,(especially in radio, microwave and other high frequency applications)and liquids are difficult to seal inside a small semiconductor packagedue to their volumetric expansion with temperature and theirincompressibility.

At the same time, current techniques for conductive cooling from asemiconductor to the semiconductor package 100 is limited by the thermalresistance of the semiconductor 105 material, the semiconductor bondingmaterials 106, their thickness the package 100 surface area and otherfactors.

Prior art heat dissipation systems use diamond, gold or silver embeddedepoxies to reduce thermal resistance of the conduction bond joint 106from the bottom of the semiconductor 105 to the package 100, but thiscan't improve the heat flow through the semiconductor.

The highest heat fluxes achievable in prior art semiconductor packages100 are attainable with packages 100 that spray cool the semiconductorpackage 100 or even directly to the surface of the semiconductor 104,where a liquid is actively sprayed in mostly vapor filled chambers 116,and the heat transfer effected by the resulting liquid to vapor phasechange. However, these approaches are “active” and are therefore morecomplicated, expensive, and prone to failure than passive designs. Suchsystems also require pressurized systems which use additional energy.Spray-cooling systems also must be designed such that there is notexcessive liquid in the semiconductor chamber 116, to avoid the liquidexpansion over large temperature ranges from over pressurizing andbursting the chamber 116.

While spray cooling techniques are capable of obtaining a maximum heatflux of a nucleate boiling point, the lack of adequate liquid in thechamber 116 pushes the heat flux from nucleate boiling region to theboiling regimes transition and film regions (towards point “D”), withgreat loss in available heat flux and higher ΔT_(e) (ΔT_(e) refers tothe temperature difference between solid surface and a liquid adjacentto the surface—for example, in a pot of boiling water, the differencebetween the temperature of the water adjacent the pot surface and thepot itself).

FIG. 1B is a plot of a pool boiling curve for water, showing the heatflux q″_(s)(watts/m²) as a function of ΔT_(e), the nucleate boilingpoint (point “C”) and boiling regimes transition and film regions (point“D”). FIG. 1B shows that 2×10⁶ watts/m² (200 watts/cm²) of heat flux isattainable at the maximum pool boiling point (point “C”). Although wateris undesirable for some applications that will be in contact withoperating semiconductor devices, de-ionized water may be used ifantifreeze and dielectric constant requirements are met.

However other fluids that are non-electrically conductive andnon-corrosive, and hence more compatible with high frequency electronicsemiconductors are available, albeit with ebullient heat transfercoefficients different than water. In one embodiment, thenon-electrically conductive fluid has a dielectric constant ofapproximately 1.85 or less. One such fluid is FLOURINERT or FC-77, whichis available from the 3M COMPANY. The heat flux available from use ofsuch a fluid in contact with the top surface of the semiconductor 104 isin addition to the heat flux available through conduction through thechip 105 and out the bottom in standard existing mounting approaches.Importantly, the liquid is in direct contact with the semiconductor's104 junction and thus it can control the actual junction temperaturemuch better than prior art methods because the density of a liquid indirect contact with the semi-conductor 104 junction is higher than a gasor a gas/liquid spray mixture.

Different non-electrically conductive electronic fluids having a rangeof boiling temperatures are available from the 3M COMPANY and others,and the designer can select the fluid based on the desired maximum chipjunction temperature, actual chip power dissipation and availablepackage size for a fluid reservoir.

The use of the non-electrically conductive liquid tends to clamp thechip's maximum junction temperature at the boiling point of thenon-electrically conductive liquid. While F-77 boils at 97 degreesCelsius, other available non-electrically conductive liquids offer otherboiling points.

The present invention provides an improved semiconductor package thathaving a chamber that, when filled, encases the semiconductor in anelectronic non-electrically conductive fluid such as 3M's FC72, FC-77and others. In the preferred embodiment, the non conductive fluidcompletely fills the cavity with no ullage (i.e. all liquid and no gas).This package has the ability to expand with the fluid volumetric changesover temperature so that the maximum heat flux point on the pool boilingcurve (point “C”) can be achieved and maintained with the resultantebullient, convection and conduction heat flow processes all moving heatsimultaneously away from the semiconductor 104 to the large packagesurface 100 area.

FIG. 2 is a diagram illustrating one embodiment of the presentinvention. In this embodiment, the semiconductor package 100 comprises aheat-generating semiconductor device 104 mounted on a semiconductor chip105. A volumetrically expandable chamber 214 is disposed to sealinglysurround the semiconductor chip 105. The volumetrically expandablechamber 105 includes an inert and non-electrically conductive liquid 216that is circulated within the chamber 105 by the generated heat of thesemiconductor device 104, thereby cooling the semiconductor device 104.In one embodiment, the dielectric constant of the non-electricallyconductive liquid is 1.85.

In the illustrated embodiment, the volumetrically expandable chamber 214is formed by a substrate or heat sink 105 coupled to the substrate (e.g.via epoxy or eutectic bond 106), and a concave structure formed by aheat-dissipating cover 204 disposed on a side of the semiconductor chip105 opposing the substrate 108 and an expandable surround structure 202sealingly coupled to the cover 216 and the substrate 108. In theillustrated embodiment, the surround structure comprises a bellows 202expandable in a direction perpendicularly away from the substrate 108.The bellows can be sealingly affixed to the substrate 108 and/or thecover 204 via an epoxy bond, a eutectic bond, or a weld 112. The cover204 may also optionally comprise a heat sink 114 to draw heat away fromthe cover 204.

The foregoing configuration provides a conductive heat path 212 awayfrom the semiconductor device 104 through the substrate/heat sink 108,but also provides convection currents 210 and ebullient currents frombubbles 208 that circulate the non-electrically conductive fluid 216within the chamber 214 and away from the semiconductor device 104,toward the cover 204 and the bellows 202 where the fluid is cooledbefore returning to the vicinity of the semiconductor device 104. Theprovision of a convection (passively) circulated non-electricallyconductive fluid 216 substantially increases the heat flux over thatwhich is possible via conductive cooling via paths 212 alone.

While the foregoing design provides effective cooling using only passivemeans (essentially using the heat from the semiconductor device 104itself as the engine to move non-electrically conductive liquid 216throughout the chamber 214), improved performance, albeit at highercost, can be obtained by actively circulating the non-electricallyconductive fluid 216 within the chamber 214 or even by pumping thenon-electrically conductive fluid to an external heat dissipation devicesuch as a radiator.

To maximize heat transfer, the chamber 214 is preferably filledcompletely with the non-electrically conductive fluid 216. Although someboiling may occur, any bubbles 208 forming from such boiling quicklymove away, create currents, transfer heat away to their surroundings,and disappear, thus creating maximum heat flow as the buoyancy of thehot bubbles 208 moves them away from the heat source.

The foregoing utilizes a “bellows cover” as the top cap of thesemiconductor package instead of a conventional ceramic, metal orplastic cover and the package is filled with electronic fluid with aboiling point tailored to the specific chip's needs (FC-72, FC-77 otherinert 3M electronic fluids, and other fluids or mixtures of fluids). Alarge surface area finned heat sink can subsequently be attached to thiscap (or the bottom, or both) to move the heat from the package to theair (or other materials) around it. So configured, the package canpassively remove three times as much heat from the semiconductor devicesas conventional packaging methods.

The structure produces this functionality by containing an electronicliquid in a hermetically sealed chamber around the semiconductor thatcan expand with the fluid's volumetric change over large temperatureranges and still maintain hermeticity.

FIG. 3 is a diagram illustrating one embodiment of how the chamber 214can be filled with the non-electrically conductive liquid 216. In thisembodiment, the substrate/heat sink 108 includes a tube 302 that is usedto fill the chamber 214. After the filling is complete, the tube 302 maybe pinched off and sealed to effect a hermetic seal at the interioropening 304 or the exterior opening 306. The tube 302 can be fashionedout of copper or any other suitable material that can be cold weldedwith a simple crimping device. If desired, the tube 302 can be builtinto the substrate/heat sink 108, whether by drilling or etchingappropriate layers. The chamber 214 may also be oriented while beingfilled so that no air gaps remain when the process is completed. Vacuumfilling techniques can also be used in which a vacuum is applied throughthe tube to evacuate the chamber 214, the valved off, and a second valveopened to a liquid reservoir storing the degassed non-electricallyconductive liquid 216. The non-electrically conductive liquid 216 flowsinto the evacuated chamber 214 with no air pockets or bubbles. Thesecond valve is then closed and the tube crimped to seal the chamber214. Degassing of the liquid is accomplished by placing the liquid in avessel and evacuating the vessel to remove any gas.

FIGS. 4-8 are diagrams depicting alternate embodiments of the improvedsemiconductor package.

FIG. 4 is a diagram illustrating an embodiment wherein the semiconductorpackage 100 uses a flip-chip configuration. In this configuration, thesemi conductor device is disposed on a bottom side of the semiconductorchip 105 (e.g. facing the substrate/heat sink 108), and thesemiconductor chip 105 is coupled to the substrate/heat sink 108 viastandoffs 402. In this configuration, the conductive heat paths 212 mustpass through the standoffs, but the passively circulated convective flowcan pass from the semiconductor device 104, around the substrate 105, upto the cover 204, around the bellows 202 and back to the semiconductorchip 104.

FIG. 5 is a diagram illustrating an embodiment in which thevolumetrically expandable chamber 214 is formed by structures comprisingthe substrate/heat sink 108, the heat dissipating cover 204, a surroundstructure 506 sealingly coupled to the cover and the substrate, and avolumetrically expandable auxiliary chamber 504 in fluid communicationwith the volume enclosed by the cover 204, surround structure 506 andsubstrate/heatsink 108 via an aperture 502. In the illustratedembodiment, the aperture 502 and auxiliary chamber 504 are disposed on aside of the surround structure 502, however, aperture 502 and auxiliarychamber 504 may instead be disposed through and adjacent the cover 204or even the substrate/heat sink 108. Also in the illustrated embodiment,the volumetrically expandable auxiliary chamber 504 comprises aexpanding bellows, however, any structure that permits volumetricexpansion can be used. For example, the auxiliary chamber 504 maycomprises a structure fashioned from stretchable material such asrubber.

As was the case in the above illustrated embodiments, the embodimentshown in FIG. 5 uses both conventional conduction cooling paths 212 andconvection cooling using the non-electrically conductive liquid 216 incontact with the semiconductor device 104 and completely filling thecavity 214 to cool the semiconductor device 104.

FIG. 6 is an illustration of another embodiment of the invention inwhich a plurality of semiconductor devices 104A-104C (hereinaftercollectively referred to as semiconductor devices 104) and chips105A-105C (hereinafter collectively referred to as chips 105) are bondedto a single substrate/heat sink 108 via multiple bonds 106A-106C((hereinafter collectively referred to as bonds 106). In thisembodiment, the volumetrically expandable chamber 214 encloses theplurality of semiconductor devices 104 and chips 105A, again providingconventional conductive cooling and passive convection cooling using thenon conductive liquid 216 in contact with the semiconductor chip.

FIG. 7A is an illustration of another alternate embodiment of theinvention in which multiple semiconductor assemblies 102A-102C(hereinafter referred to as semiconductor assemblies 102) with separatesubstrates are disposed in the volumetrically expandable chamber 214. Inthis embodiment, the semiconductor assemblies 102 are coupled to achamber plate/heatsink 710, and the chamber 214 is formed by a rigidsurround structure 708 sealingly coupled to the chamber plate/heatsink710 and a cover 702 sealingly coupled to the surround structure.Volumetric expandability is provided by ducting the non-electricallyconductive fluid 216 from the chamber 216 to the auxiliary chamber 504via duct 706, thereby providing fluid communication between the chamber214 and the auxiliary chamber. This embodiment may also be practiced bysubstituting an expandable bellows structure for the rigid surroundstructure 708. This would obviate the need for the duct 706 and theauxiliary chamber 504.

FIG. 7B is an illustration of an embodiment in which thenon-electrically conductive liquid is actively circulated within thevolumetrically expandable chamber 214. In this embodiment, the fluidpump 752 is provided access to the liquid 216 in the chamber 214 viajoint 750. The pump 752 cools the liquid 216 by pumping it through aradiator/heat exchanger 754 for cooling purposes. The cooled liquid 216is then provided to the chamber 214, where it is used to cool thedevice(s).

FIG. 8 is a diagram of a further alternate embodiment of the invention.In this embodiment each semiconductor assembly 102 is disposed on anindividual chamber plate 806A-806C (hereinafter collectively referred toas chamber plates 806), and the volumetrically expandable chamber 214comprises a plurality of sub-chambers 810A-810C, each formed by thecorresponding individual chamber plate 806, individual surroundstructure 804, and the community cover 702, hermetically sealed to oneanother. As was the case in the embodiment illustrated in FIG. 7, thecover 702 includes a duct 706 in fluid communication with avolumetrically expandable auxiliary chamber 504 and the chamber 214.However, in this embodiment, the duct 706 comprises a plurality ofopenings 802A-802C, each of which providing fluid communication betweenthe sub-chambers 804A-804C and the auxiliary chamber 504 and each other.

CONCLUSION

This concludes the description of the preferred embodiments of thepresent invention. The foregoing description of the preferred embodimentof the invention has been presented for the purposes of illustration anddescription. It is not intended to be exhaustive or to limit theinvention to the precise form disclosed. Many modifications andvariations are possible in light of the above teaching. For example, thecooling capacity of any of the foregoing designs can be increased usingsecondary cooling techniques to cool the package via thermal exchangewith the heat sink, substrate, and/or bellows. Such secondary coolingtechniques can include, for example (1) directing a flow of air over thepackage (e.g. by use of a fan, or by placing the package in a locationsubject to a flow of air during operation), (2) directing a flow ofanother fluid over the package (for example, by placing at least part ofthe package in thermal contact with a fuel line), and/or by (3) placingone or more portions of the package in thermal contact with heatconductive structural members. It is intended that the scope of theinvention be limited not by this detailed description, but rather by theclaims appended hereto. The above specification, examples and dataprovide a complete description of the manufacture and use of thecomposition of the invention. Since many embodiments of the inventioncan be made without departing from the spirit and scope of theinvention, the invention resides in the claims hereinafter appended.

1. A semiconductor package, comprising: a semiconductor chip having atleast one heat-generating semiconductor device; and a volumetricallyexpandable chamber disposed to sealingly surround the semiconductorchip, the volumetrically expandable chamber entirely filled with anon-electrically conductive liquid in contact with the semiconductordevice and circulated within the volumetrically expandable chamber atleast in part by the generated heat of the at least one semiconductordevice to cool the at least one semiconductor device; wherein thesemiconductor chip is coupled to a substrate; and the volumetricallyexpandable chamber is formed by structures comprising a concavestructure sealingly coupled directly to the substrate on a substratesurface facing the semiconductor chip.
 2. (canceled)
 3. Thesemiconductor package of claim 1, wherein the concave structure furthercomprises: a heat-dissipating cover disposed on a side of thesemiconductor chip opposing the substrate; and an expandable surroundstructure sealingly coupled to the cover and the substrate, theexpandable surround structure surrounding the substrate.
 4. Thesemiconductor package of claim 3, wherein the surround structurecomprises a bellows expandable in a direction perpendicularly away fromthe substrate.
 5. The semiconductor package of claim 4, wherein thebellows is sealingly affixed to the substrate via a bond selected fromthe group comprising: an epoxy bond; a eutectic bond; and a weld.
 6. Thesemiconductor package of claim 1, wherein the concave structurecomprises: a cover disposed on a side of the semiconductor chip opposingthe substrate; a surround structure sealingly coupled to the cover andthe substrate on a surface facing the semiconductor chip; avolumetrically expandable auxiliary chamber in fluid communication withthe volume enclosed by the cover, surround structure and substrate. 7.The semiconductor package of claim 6, wherein the volumetricallyexpandable chamber sealingly surrounds a plurality of semiconductorchips.
 8. The semiconductor package of claim 1, wherein thevolumetrically expandable chamber sealingly surrounds a plurality ofsemiconductor chips.
 9. The semiconductor package of claim 1, wherein:the semiconductor package further comprises: a second semiconductor chiphaving at least one second heat-generating semiconductor, the secondsemiconductor chip coupled to a second substrate; the structures furthercomprise a second concave structure sealingly coupled directly to thesecond substrate on a second substrate surface facing the secondsemiconductor chip; a community cover disposed on a side of thesemiconductor chip and the second semiconductor chip, the integratedcover having passages permitting fluid communication between a firstcavity formed by the concave structure, the substrate and the cover, asecond cavity formed by the second concave structure, the secondsubstrate and the cover; and a volumetrically expandable auxiliarychamber, coupled to the passages to permit the volumetric expansion ofthe non-electrically conductive liquid.
 10. The semiconductor package ofclaim 1, wherein the non-electrically conductive liquid is circulatedwithin the volumetrically expandable chamber solely by convectioncurrents from heat generated within the volumetrically expandablechamber.
 11. The semiconductor package of claim 1, wherein thenon-electrically conductive liquid is further circulated within thevolumetrically expandable chamber by active means.
 12. The semiconductorpackage of claim 1, wherein the non-electrically conductive liquidheated by the at least one semiconductor device remains in a freeconvection or nucleate boiling regime.
 13. The semiconductor package ofclaim 1, wherein the non-electrically conductive liquid has a dielectricconstant of approximately 1.85.
 14. The semiconductor package of claim1, wherein the semiconductor chip is coupled to the substrate in a flipchip configuration.
 15. The semiconductor package of claim 1, whereinthe substrate comprises a tube for filling the volumetrically expandablechamber with the non-electrically conductive liquid.
 16. A method ofcooling a heat-generating semiconductor device, comprising the steps of:sealingly surrounding the semiconductor device in a volumetricallyexpandable chamber; entirely filling the volumetrically expandablechamber with a non-electrically conductive liquid that contacts thesemiconductor device; and passively circulating the non conductiveliquid within the volumetrically expandable chamber by the generatedheat from the semiconductor device to cool the semiconductor device. 17.The method of claim 16, wherein: the semiconductor chip is coupled to asubstrate; and the volumetrically expandable chamber is formed bystructures comprising a surface of the substrate facing thesemiconductor chip.
 18. The method of claim 17, wherein the structuresfurther comprise: a heat-dissipating cover disposed on a side of thesemiconductor chip opposing the substrate; and an expandable surroundstructure sealingly coupled to the cover and the substrate.
 19. Themethod of claim 18, wherein the surround structure comprises a bellowsexpandable in a direction away from the substrate.
 20. The method ofclaim 16, wherein the non-electrically conductive liquid heated by theat least one semiconductor device remains in a free convection ornucleate boiling regime.
 21. A method of cooling a semiconductor device,comprising the steps of: absorbing heat from a semiconductor device viaa non-conductive inert liquid in contact with the semiconductor device;sealingly enclosing the semiconductor device and the non-electricallyconductive inert liquid in a volumetrically expandable chamber; andpassively circulating the non-electrically conductive inert liquidwithin the volumetrically expandable chamber at least in part by theheat drawn from the semiconductor device.